Modelling experimental conditions for strong field ionisation using R-Matrix with time-dependence calculations

This method, validated using two different experimental regimes, helps (1) distinguish features of the experimental spectrum attributable to the single-atom response and (2) predict which single-atom spectral features may be observed experimentally.<br><br>Chapter 5 extends this method to two-colour, pump-probe laser schemes, discussing the additional considerations. It assesses the feasibility of observing an XUV-initiated high harmonic generation (XIHHG) mechanism and applies the method to intensity-average RMT calculations for ATAS.<br><br>Chapter 6 uses ATAS to explore sub-cycle structures in absorption lines in xenon during strong field ionisation.

By analysing the phase of the absorption lines (both experimentally and via RMT calculations) alongside depletion of the ground state, a second ionisation pathway, dubbed 'XUV-assisted strong-field ionisation,' is identified as interfering with the direct ionisation pathway. Chapter 7 extends this work to address subtle differences between the experimental and theoretical results, offering an alternative presentation of absorption line-shapes and exploring the nature of the second ionisation pathway introduced in Chapter 6, by linking the observed interference pattern with residual ion populations from RMT calculations.